I'm interpreting the OP's intent differently than most here. I think he is asking about what's best for the motorhome being stored instead of while he's living in it.
I have a similar situation here in coastal georgia with my motorhome stored in partial sun and it's really humid here! When we're not using the motorhome, I just run a dehumidifier sitting in the kitchen sink set as Wolfe10 suggested at 45%. I leave the valve open so it can drip outside.
When we're using the motorhome, the dehumidifier stays home and we run the roof air.
Fred